The mining, oil, and gas industries drill boreholes in the subsurface of the Earth, with some boreholes exceeding a few miles. Through such boreholes, also called wellbores, oil and/or gas can be collected from deep within the Earth formations. However, many physical challenges often must be overcome in order to collect such hydrocarbons and any other fluids. For example, the walls of the borehole may collapse or fracture in an undesired manner, which can cause a wellbore to cease production. Even if a wellbore does not collapse, a nearly ubiquitous problem is the production of sand from inside the wellbore.
Sand production is a process in which small particles of rock or other subsurface materials move from the wellbore wall, or from within pores or fractures in the wellbore and from perforations in the wall, into the flow of fluids produced by the wellbore. Thus, the oil or gas collected at the oil rig through the wellbore is contaminated with sand. Sand in collected fluids can cause many problems, including a requirement to remove the sand from the fluid, a requirement to clean the sand of fluids once the sand is removed, sand-induced wear and tear on equipment, erosion and ultimate collapse of the wellbore itself, and many other problems. As a result, the oil and gas industry spends many billions of dollars each year on equipment and technologies to deal with produced sand and on equipment and technologies to mitigate sand production.
One method of mitigating sand production is to predict when sand will be produced at a particular well. Armed with the knowledge of when sand production will occur in a particular wellbore, engineers can avoid actions that will lead to sand production. Alternatively, if sand production is unavoidable, engineers can set up selected sand control procedures and equipment in such a way as to maximize the production of fluids, minimize the production of sand, and deal with sand that is produced.
As described further below, some techniques for predicting sand production are known. However, sand production has a variety of causes, some of which depend on factors that are unique to each wellbore. Hence, sand production can be very difficult to predict accurately.
However, the oil and gas industry considers accurate prediction of sand production to be very important. Implementation of sand mitigation systems or sand control systems is very expensive, and should be avoided if possible. Additionally, the correct sand mitigation systems or sand control systems for a particular wellbore should be chosen from many available systems. Furthermore, potentially catastrophic consequences of failing to predict sand production accurately can occur, such as the complete failure of a wellbore and possibly a drilling site. If a failed drilling site is a relatively immovable off-shore oil rig, then failure to predict sand production accurately potentially can result in the loss of billions of dollars. To date, no complete solution exists for accurately predicting when, and under what in-situ stress conditions, sand will be produced at any given wellbore. Specifically, existing models can not predict deformation and compaction-induced change of strength characteristics that trigger sand production.